1. Field of the Invention
The present invention relates to a magnetoresistance effect element and a magnetic memory.
2. Related Art
Magnetoresistance effect elements using magnetic material films are used in, for example, magnetic heads and magnetic sensors. In addition, it is proposed to use the magnetoresistance effect elements in solid state MRAMs (Magnetic Random Access Memories).
As a magnetoresistance effect transistor element which has a sandwich structure film formed by inserting a single layer of a dielectric between two ferromagnetic layers, which causes a current to flow perpendicularly to the film surface, and utilizes a tunnel current, the so-called “ferromagnetic TMR (Tunneling Magneto-Resistance effect) element” is proposed. Since it has become possible to obtain a magnetoresistance change rate of at least 20% in the ferromagnetic tunneling magneto-resistance effect element, technical development for commercial application of the element to the MRAM is being conducted vigorously.
This TMR element can be implemented by forming a thin Al (aluminum) layer having a thickness in the range of 0.6 nm to 2.0 nm on a ferromagnetic electrode, then exposing a surface of the Al layer to oxygen glow discharge or oxygen gas, and thereby forming a tunnel barrier layer made of AL2O3 or a tunnel barrier layer formed as a thin film having a thickness in the range of 0.5 nm to 3.0 nm made of MgO (magnesium oxide).
A ferromagnetic single tunnel junction having a structure obtained by providing one of the ferromagnetic layers having the tunnel barrier layer therebetween with an antiferromagnetic layer and using the ferromagnetic layer as a magnetization pinned layer is proposed.
Furthermore, a magnetic tunnel junction having magnetic particles dispersed in a dielectric, and a ferromagnetic double tunnel junction (continuous film) are also proposed.
These magnetoresistance effect elements also have a possibility of being applied to the MRAMs because it has become possible to obtain a high magnetoresistance change rate and the decrease of the magnetoresistance change rate is suppressed even if the voltage value applied to the magnetic tunnel junction is increased to obtain a desired output voltage value.
The magnetic recording element using the ferromagnetic single tunnel junction or the ferromagnetic double tunnel junction is non-volatile, and has a potential that a write and read time is as fast as 10 nanoseconds or less and the number of times of rewriting is also at least 1015.
As regards the cell size of the memory, however, there is a problem that the size cannot be made smaller than a semiconductor DRAM (Dynamic Random Access Memory) or less when using an architecture in which a memory cell is formed of one transistor and one TMR element.
In order to solve this problem, a diode type architecture including a series connection composed of a cell formed of a TMR element and a diode between a bit line and a word line and a simple matrix type architecture obtained by arranging cells each having a TMR element between a bit line and a word line are proposed.
In either case, however, there are the following problems. Inversion is conducted using a current magnetic field based on a current pulse when writing to the magnetic recording layer is executed, resulting in high power consumption. When the capacity is increased, there is a limit in allowable current density for wiring and consequently a large capacity cannot be obtained. The area of the driver for letting a current flow increases.
In order to solve the above-described problem, a solid-state magnetic memory having a thin film formed of a high permeability magnetic material around writing wiring is proposed. According to these magnetic memories, a high permeability magnetic film is provided around wiring, and consequently a current value required to write information into the magnetic recording layer can be reduced efficiently. Even if they are used, however, it is very difficult to cause the write current value to become 1 mA or less.
In order to solve these problems, a write method using a spin injection method is proposed (see, for example, U.S. Pat. No. 6,256,223). This write method utilizes inversion of magnetization of the magnetic recording layer in the magnetoresistance effect element obtained by injecting a spin-polarized current into the magnetoresistance effect element.
When conducting spin injection by using the writing method utilizing spin injection, spin inversion does not occur unless a current having a very high current density is let flow to the element. If a current having a high current density is let flow to a magnetoresistance effect element having a tunnel barrier layer, a high electric field is applied to the tunnel barrier layer and consequently element destruction is caused. Therefore, a structure in which spin injection is conducted at a low current density is demanded.
In addition, it is also needed that the spin inversion current density is low to reduce the write current.
As heretofore described, the spin injection method involving operation conducted at a low write current requires an element in which spin inversion is conducted at a low current density.